Magnetron having concentric annular tunable resonator utilizing axial plunger and vacuum sealing bellows mounted inside principal envelope wall



3,263,118 ONCENTRIC ANNULAR TUNABLE RESONATOR ER AND VACUUM SEALING BELLOWS L L A w E w L L A E T V N E E a m L m S m. A E m P P w H .0 PN HGMI m w V MT m w G N N m I Z I n Gw 6 9 1 6 Z Y m J z Sheets-Sheet 1 Filed July 30, 1953 INVEKNTORS Howard F? Peosley and Allan J. Bomford ATTORNEY July 26, 1966 H. P. PEASLEY ETAL 3,

MAGNETRON HAVING CONCENTRIC ANNULAR TUNABLE RESONATOR UTILIZING AXIAL PLUNGER AND VACUUM SEALING BELLOWS MQUNTED INSIDE PRINCIPAL ENVELOPE WALL Filed July 30, 1963 2 Sheets-Sheet 2 /54 Fig 2.

United States Patent vania Filed July 30, 1963, Ser. No. 298,775 Claims. (Cl. 315-3955) This invention relates to electron discharge devices, especially those of the coaxial magnetron type, and more particularly to a tuning mechanism for use in such devices.

Most coaxial magnetrons result in a device whose physical size is appreciably larger than a comparable conventional type magnetron. One of the major causes of this increase in size resides in the tuning mechanism for the outer cavity resonator. In a coaxial magnetron, tuning is normally accomplished by changing the axial length of the outer cavity resonator through the utilization of an electrically conductive plate which is movably positioned therein. Because the outer cavity resonator must be maintained in vacuum, the coaxial magnetron normally contains quite a large vacuum volume. Additionally, such a device is usually plagued with a great number of reentrant regions associated with the tuning mechanism and as such may be very difficult to evacuate.

It is, therefore, an object of the present invention to provide an improved electron discharge device.

A further object is to provide an improved coaxial magnetron.

Another object is to provide an improved tuning system for a coaxial magnetron.

Another object is to provide a coaxial magnetron of compact size and reduced vacuum volume.

Still another object is to provide a tunable coaxial magnetron having a minimum number of reentrant regions in the vacuum portion.

A still further object is to provide a coaxial magnetron with a minimum of back cavity resonances.

Briefly, the present invention provides a coaxial magnetron having an outer cavity resonator which is tunable through the movement therein of an electrically conductive plate. The improved design of the present invention provides that substantially entire mechanism for effectting the movement of this plate is positioned outside the vacuum portion of the device. This improved design not only reduces the total vacuum volume of the device but also serves to simplify the construction as a fewer number of movable vacuum seals are necessary.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of the specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is a perspective view, partially in section and partially broken away of a coaxial magnetron embodying the present invention;

FIG. 2 is a side view in elevation of the device of FIG. 1 to which appropriate magnets have been added; and,

FIG. 3 is a fragmentary view, partially in section and partially broken away showing a vmodification of the design of the device of FIG. 1.

With reference now to FIGS. 1 and 2, there is shown a coaxial magnetron embodying the present invention. The magnetron is comprised of a body member which is substantially cup-shaped and includes a substantially cylindrical side wall 12 and a bottom 14 of a suitable 3,263,113 Patented July 26, lgfifi electrically conductive material such as copper. Centrally disposed within the body 10 is a cathode 16 which includes a sleeve member 18 of suitable material such as molybdenum having thereon an electron emissive coating 20 of a suitable material suchas barium oxide. Surrounding the cathode 16 is a substantially cylindrical anode 22 having a plurality of vanes 24 which extend radially inwardly therefrom. The planes of the anode vanes 24 are inclusive of the axis of the cylindrical anode 22 and define in cooperation with the anode 22 an array of anode cavity resonators 26. Coupling slots 28 extend through the cylindrical anode 22 and are centered between adja cent anode vanes 24. The slots communicate with alternate ones of the cavity resonators 26.

The cylindrical wall portion 12 of the body 10 and the cylindrical anode 22 along with the bottom portion 14 of the body 19* define, in part, an outer cavity resonator 30. Extending through the wall 12 such as to communicate with the outer cavity resonator 3G is an output coupling slot 32. The coupling slot 32 serves as a means through which energy may be removed from the outer cavity resonator 30 and has been shown in its simplest form. for purposes of simplicity.

Positioned atop the cup-shaped body member 10 is a substantially disk-shaped cover means 34. The cover 34 is of a suitable non-magnetic material such as stainless steel and is vacuum sealed at its periphery to the cylindrical wall portion 12. While any number of vacuum seals may be utilized, in the present embodiment this seal is efiected through the use of a ring 3 6, of a material such as stainless steel, which is fitted within a removed portion 38 within the upper outer edge of the wall 12. Through a suitable annular braze do, the ring 38 is vacuum sealed to the wall 12. The inner diameter of the ring 38 is approximately equal to the outer diameter of the disk 34 and a vacuum. seal may be effected between these two members by a welding operation at their juncture 42.

Tuning in coaxial magnetrons is accomplished by axially moving an electrically conductive member within the outer cavity resonator. In the present invention, this conductive member is an annular or tuning member 44, of suitable material such as copper, which is substantially U-shaped in cross-sectional area. Through a suitable means which will be discussed in detail later, the tuning member 44 is given movement axially within the outer cavity resonator 30.

The magnetic circuit in the present device is inclusive of two substantially identical horseshoe magnets 46, a bottom pole piece 48 and an upper pole piece 50. Also included in the magnetic circuit is a magnetic spacer 52 which is a substantially U-shaped member and which serves to connect the upper poles of the magnets 46 to the upper pole piece 50. The magnetic spacer 52 also serves as a support means for the tuning drive mechanism as will be explained later. The pole pieces 48 and 50 and the spacer 52 may be made of a suitable magnetic material such as soft iron.

In accordance with the present invention, the tuning member 44 is actuated by means entirely exterior to the vacuum portion of the system. The means for effecting the movement of the member 44 includes a bearing support 54 which may be secured to the upper edges of the U-shaped member 52 by means of a plurality of screws 56. The bearing support is of a suitable non-magnetic material such as stainless steel and is provided with a longitudinally extending bore 57 into which is fitted a sleeve bearing member 58. The bearing member 53 may be made of a suitable self-lubricating material such as carbon impregnated bronze and may be in the form of a hollow cylindrical member which is press fitted into the bore 57 of the support 54. An actuating rod 60 is slidably retained within the bearing 53 and capable of reciprocal motion therein. The actuating rod 66 is given reciprocal motion by any suitable means, such as a screw drive, which (for the purpose of simplicity has been omitted from the drawing. Affixed to the lower end of the actuating rod 6t is a cross member 62. The two members 60 and 62 form substantially a T-shaped assembly. Secured to either end of the cross member 6'2 and firmly affixed thereto are two rod members 64 which extend thnough suitable apertures 66 within the cover 34. The other ends of the rods 64 are securely aflixed to the annular member 44.

In the illustrated embodiment, the upper pole piece 50 is vacuum sealed to the cover 34 and is provided with an extension portion 68 which extends above the cover 34, through an aperture 70 centrally located within the cross member 62 and into a centrally extending bore 72 within the actuating rod 60. While, this particular arrangement is primarily for purposes of initial alignment, it is also possible that this extension of the extension portion 68 into the bore 72 may act as an additional bearing surface for the actuating rod 60. Additionally, as is obvious, it would be entirely possible and feasible to provide the internal bore 72 of the rod 66 with a suitable bearing surface and as such this surface cooperating with the extension 68 of the pole piece 50 would serve as the only bearing for the rod 60.

In the embodiment illustrated in FIG. 1, vacuum is maintained within the region of the cathode, anode and outer cavity resonator through the employment of two ring-shaped bellows 74 and 76. The outer bellows 74 has a diameter sufiicient to be positioned on the outside of the two rod members 64 while the inner bellows 76 has a diameter such as to be positioned inside of the rods 64. Each of the bellows 74 and 76 is vacuum sealed by a suitable means such as brazing at their upper and lower edges respectively to the cover 34 and the annular tuning member 44. In this manner, it is readily evident that the apertures 66 and for that matter the entire assembly for moving the tuning member 44 are not included within the vacuum system and as such it is not necessary to vacuum seal these members. As well as the exclusion of moving parts from the vacuum system, the above-described assembly provides two additional benefits which are not readily apparent. If each of the bellows 74 and 76 is made of a suitable lossy material such as stainless steel or Monel, their presence in the area above the tuning member 44 will absorb any radio frequency energy which is present within this region and will therefore prevent the establishment of the resonance in this region. This resonance is commonly known as back cavity resonance and is detrimental to the overall efficiency and operation of a coaxial magnetron. Through the use of this design, it is therefore not necessary that the fit between the member 4-4 and the side walls 12 be held to high manufacturing tolerances and hence greater ease in manufacturing is achieved.

A second feature which should be noted concerning the positioning and operation of the bellows 74 and 76 is that of applying a bias or spring loading to the tuning assembly itself. If each of the bellows is made so as to have a solid free height, the extension of the bellows through the operation of the mechanism will serve to resiliently load the entire tuning assembly and hence reduce any play therein.

FIG. 3 illustrates a second embodiment of the bellows assembly. In this embodiment, a bellows 76 is again annular but having an inside diameter slightly larger than the diameter of the rod 64 or approximately equal to the diameters of the apertures 66. Two such bellows 76 are provided, one around each of the rods 64. As before the upper and lower edges of the bellows 76 are vaccum sealed respectively to the cover 34 at the tuning plate 44. While this arrangement is perhaps easier to make inasmuch as the length of vacuum seal necessary is considerably shorter than that required in the embodiment of FIG. 1, it does not provide as much lossy material to prevent back cavity resonance. It also obviously increases the amount of volume to be evacuated.

It is seen, therefore, that there has been shown and described a coaxial magnetron of improved design and of small vacuum volume. The above-described design also provides that the moving parts are not required to be vacuum sealed but that the actuating mechanism for the tuning plate is exterior to the vacuum.

While there have been shown and described what are at present considered to be the preferred embodiments of the invention, modifications thereto will readily occur to those skilled in the art. For example, while the design illustrated is inclusive of only two rods extending and connecting with tuning plate 44 it is obvious that three or more r-ods could be used for greater stability without affecting the vacuum portion.

It is not desired, therefore, that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

We claim as our invention:

1. A coaxial magnetron comprising a centrally disposed cathode, a cylindrical anode including a plurality of anode resonators circularly positioned about said cathode, a cylindrical wall concentric with and spaced from said cylindrical anode, said cylindrical wall and said anode defining an outer cavity resonator of substantially annular cross-section, an annular member of electrically conductive material disposed and axially movable within said outer cavity resonator, end plate means vacuum sealed to said cylindrical wall, operating means extending through said end plate means and connected in an operative relationship with said annular member to effect said axial movement thereof, and hollow means comprising a first ring-shaped member of lossy material extending between and vacuum sealed to the outer periphery of said annular member and said end plate means and a second ring-shaped member of lossy material extending between and vacuum sealed to the inner periphery of said annular member and said end plate means, said operating means connected to said annular member between said first and second ring-shaped members.

2. A coaxial magnetron comprising a centrally disposed cathode, a cylindrical anode including a plurality of anode resonators circularly positioned about said cathode, a cylindrical wall surrounding said anode resonators, said cylindrical wall and said anode defining an outer cavity resonator of substantially annular cross section, a tuning member positioned within said outer cavity, a first and second end plate closing the end portions of said cylindrical wall, a first magnetic pole piece member extending through a centrally located aperture in said first end plate and provide-d with a vacuum seal between said first end plate and said first pole piece, a second pole piece extending through said second end plate and provided with a vacuum seal between said second end plate and said second pole piece, means for adjusting said tuning member including rod members extending through apertures provided in said second end plate and secured to said tuning member, bellows means for providing and permitting movement of said rod members, said second pole piece having a U-shaped extension projecting above the surface of said second end plate and positioned between said rod members, the legs of said U-shaped members providing faces for magnets, a cross piece member secured to said rod members and positioned within said U-shaped extension and means for moving said cross piece member and for adjusting the position of said tuning member within said outer cavity resonator.

3. A coaxial magnetron comprising a centrally disposed cathode, a cylindrical anode including a plurality of anode resonators circularly positioned about said cathode, a cylindrical wall surrounding said anode resonators, said wall and said anode defining an outer cavity resonator of substantially annular cross section, an annular tuning member positioned within said outer cavity resonator, a first and second end plate closing the end portions of said cylindrical wall, a first magnetic pole piece member extending through a centrally located aperture in said first end plate and provided with a vacuum seal between said first end plate and said pole piece, a second pole piece extending through said second end plate and provided with a vacuum seal between said second end plate and said pole piece, a U-shaped magnetic pole piece extension provided exterior of said second end plate, said second pole piece extending through the central portion of said U-shaped extension and secured thereto, tuning means for moving said tuning member positioned exterior of said second end plate and provided with nonmagnetic rods extending through apertures provided in said second end plate and secured to said tuning member, bellows means to provide a vacuum seal of said apertures and permit movement of said rods, 2. non-magnetic cross-piece member secured to said tuning rods and slidably engaged with said second pole piece and non-magnetic support means secured to said U-shaped pole piece extension and to said cross piece member to provide relative movement of said cross piece member and tuning rods in an axial direction and slidable upon said second pole piece for adjusting the position of said tuning member within said outer cavity resonator.

4. A coaxial magnetron comprising a centrally disposed cathode, a cylindrical anode including a plurality of anode resonators circularly positioned about said cathode, a cylindrical wall surround-ing said anode resonators, said cylindrical wall and said anode defining an outer cavity resonator of substantially annular cross section, a tuning member positioned within said outer cavity resonator, first and second end plates closing the end portions of said cylindrical Wall, a first magnetic pole piece member extending through a centrally located aperture in said first end plate and provided with a vacuum seal between said first end plate and said first pole piece, a second pole piece extending through said second end plate and provided with a vacuum seal between said second end plate and said second pole piece, means for adjusting said tuning member including rod members extending through apertures provided in said second end plate and secured to said tuning member, bellows means for providing a vacuum seal and permitting movement of said rod members, said bellows means having a solid free height, said second pole piece having extensions thereon exterior of said second end plate to provide a first and second pole face, a cross piece member secured to said rod members and positioned and movable between said first and second pole faces and means for moving said cross piece member for adjusting the position of said tuning member within said outer cavity resonator.

5. A coaxial magnetron comprising a centrally disposed cathode, a cylindrical anode including a plurality of anode resonators circularly positioned about said cathode, a cylindrical wall surrounding said anode resonators, said cylindrical wall and said anode defining an outer cavity resonator of substantially annular cross section, an annular tuning member positioned within said outer cavity resonator, first and second end plates closing the end portions of said cylindrical wall, a first magnetic pole piece member extending through a centrally located aperture in said first end plate and provided with a vacuum seal between said first end plate and said first pole piece, a second pole piece extending through said second end plate and provided with a vacuum seal between said second end plate and said second pole piece, a magnetic pole piece extension of said second pole piece provided exterior of said second end plate to provide a planar pole face offset from said second pole piece, tuning means for moving said tuning member positioned exterior of said second end plate and provided with non-magnetic rods extending through apertures provided in said second end plate and secured to said tuning member, bellows means to provide a vacuum seal of said aperture and permit movement of said rods, a non-magnetic cross piece member secured to said rods and slidably engaged on said second pole piece and movable between said pole piece extension and said second pole piece, a non-magnetic support means secured to said pole piece extension and to said cross piece member to provide relative movement of said cross piece member and said rods in an axial direction slida'ble upon said second pole piece for adjusting the position of said tuning member within said outer cavity resonator.

References Cited by the Examiner UNITED STATES PATENTS 2,227,372 12/1940 Webster et al. 333--83 2,692,977 10/1954 Koppel 333-83 2,854,603 9/1958 Collier et a1 315--3'9.77 3,032,681 5/ 196 2 Scanzani 31539.61

ELI LIEBERMAN, Primary Examiner.

GEORGE N. WESTBY, HERMAN KARL SAALBACH,

Examiners.

F. A. ADAMS, S. CHATMON, JR., Assistant Examiners. 

1. A COAXIAL MAGNETRON COMPRISING A CENTRALLY DISPOSED CATHODE, A CYLINDRICAL ANODE INCLUDING A PLURALITY OF ANODE RESONATORS CIRCULARLY POSITIONED ABOUT SAID CATHODE, A CYLINDRICAL WALL CONCENTRIC WITH AND SPACED FROM SAID CYLINDRICAL ANODE, SAID CYLINDRICAL WALL AND SAID ANODE DEFINING AN OUTER CAVITY RESONATOR OF SUBSTANTIALLY ANNULAR CROSS-SECTION, AN ANNULAR MEMBER OF ELECTRICALLY CONDUCTIVE MATERIAL DISPOSED AND AXIALLY MOVABLE WITHIN SAID OUTER CAVITY RESONATOR, END PLATE MEANS VACUUM SEALED TO SAID CYLINDRICAL WALL, OPERATING MEANS EXTENDING THROUGH SAID END PLATE MEANS AND CONNECTED IN AN OPERATIVE RELATIONSHIP WITH SAID ANNULAR MEMBER TO EFFECT SAID AXIAL MOVEMENT THEREOF, AND HOLLOW MEANS COMPRISING A FIRST RING-SHAPED MEMBER OF LOSSY MATERIAL EXTENDING BETWEEN AND VACUUM SEALED TO THE OUTER PERIPHERY OF SAID ANNULAR MEMBER AND SAID END PLATE MEANS AND A SECOND RING-SHAPED MEMBER OF LOSSY MATERIAL EXTENDING BETWEEN AND VACUUM SEALED TO THE INNER PERIPHERY OF SAID ANNULAR MEMBER AND SAID END PLATE MEANS, SAID OPERATING MEANS CONNECTED TO SAID ANNULAR MEMBER BETWEEN SAID FIRST AND SECOND RING-SHAPED MEMBERS. 